This invention relates to liquid filtration and more particularly to an improved filter for use with a pressurized oil system, e.g. with a diesel engine.
Commonly, diesel engines are provided with a pressurized oil system which includes a by-pass filter. The by-pass filter takes a portion of the oil from the oil pump outlet, filters it, and returns it to the diesel engine. The by-pass filter includes a housing with a filter pack therein. The flow rate through the filter pack is determined by resistance to fluid flow. The filter pack is rather dense, for example, wood chips and ground cellulose within a cylindrical metal shell, and forms fine pathways for removing finely dispersed contaminates from fluid flow. It is relatively hard to force oil through the filter pack, particularly when the oil is cold. When the oil is wormed, the viscosity is reduced and it is easier for oil to flow through the filter pack. To increase the speed of filter pack warm up, a by-pass hole or orifice is provided in a cylindrical member extending within the filter pack and communicating with an oil outlet from the housing. When the oil is cold, it will take the path of least resistance and flow from the oil inlet in the housing, through the by-pass orifice, and exit the housing through the oil outlet. As the oil is warmed, more oil will pass through the filter pack. At operating temperature, it is intended all oil will pass through the filter pack.
However, by-pass orifice design is presently a design tradeoff, with an attendant failure to optimize operating efficiency of the filter pack. To warm up the oil as quickly as possible, the by-pass orifice should be as big as possible. On the other hand, for highest operating efficiency, the by-pass orifice should be as small as possible to preclude by-pass of oil after the oil has reached a predetermined operating temperature. Even at or above operating temperature, some oil will bypass the filter pack, with a resultant decrease in operating efficiency of the filter pack.
To improve upon existing by-pass filters, there has been conceived a unique by-pass filter incorporating a thermostatically controlled valve means which bypasses more oil during cold starts and which bypasses no oil during normal operation, whereby the filter pack filters virtually all the oil entering the filter housing.
The by-pass filter normally includes a fluid control orifice in the cylindrical member or hold down stand. The final control orifice is relocated to the inlet fitting in the present invention so as to lower housing pressure without affecting fluid flow. Reduction in housing pressure reduces the possibility of leaks from the housing.
An object of the present invention is to provide an improved by-pass filter which overcomes deficiencies and disadvantages of prior by-pass filters.
Another object of the present invention is to provide a by-pass filter with a thermostatically controlled valve means which bypasses more oil about the filter pack during cold start than a conventional prior art by-pass filter and which bypasses no oil about the filter pack during normal operation.
Yet another object of the present invention is to provide an improved by-pass filter incorporating relatively large by-pass orifice means for passing more oil during initial or cold start of the by-pass filter and a thermostatic valve which is open at initial or cold start and which closes when the oil reaches a predetermined temperature so that no oil is bypassed and all oil passes through the filter pack and is filtered.
Still another object of the present invention is to provide an improved by-pass filter incorporating a thermostatically controlled valve means in the holddown stand and incorporating a flow control orifice in the fluid inlet.
Other objects and advantages of the invention will become more apparent hereinafter.